In order to enhance the plugging performance of oil-based drilling fluids， a hybrid core-shell calcium carbonate-polyurethane well wall reinforcer was prepared via hydrothermal synthesis using calcium chloride，sodium carbonate， glutamic acid，2，4-toluene diisocyanate and dibutyltin dilaurate as raw materials. The effects of well wall reinforcer dosage on the rheological properties，stability and plugging performance of base slurry were investigated by measuring rheological parameters， demulsification voltage，filtration loss and invasion depth. The well wall reinforcer was compounded with some materials such as potassium titanium oxide fibers，sepiolite，diatomite and asphalt oxide. The effects of the compounded well wall reinforcer on the wetting properties，rheological properties，stability，plugging performance，and temperature resistance of the oil-based drilling fluids were studied. The results showed that the well wall reinforcer，with polyurethane as the shell and calcium carbonate microsphere as the core，had a microsphere diameter about 2 μm，exhibited minimal influence on the rheological properties and stability of base slurry，and significantly improved the plugging performance of base slurry. A dosage of 2.5%—3.0% achieved good plugging effects，with a demulsification voltage of 525—542 V and an invasion depth of 0.6 cm. The compounded well wall reinforcer with optimum formula significantly improved the wetting properties of oil-based drilling fluids，had little influence on the rheological properties of base slurry，and helped enhance stability. The demulsification voltage increased to 637 V. The various components of the compounded well wall reinforcer exerted synergistic effects，effectively plugging cracks with different pore sizes，and then exhibited good filtration loss performance. The filtration loss and invasion depth at room temperature were 1.0 mL and 0.2 cm，respectively. After aging at 180 ℃ for 8 hours，the compounded well wall reinforcer still maintained good filtration loss performance. The filtration loss and invasion depth were 3.3 mL and 0.3 cm，respectively，indicating good temperature resistance. The polyurethane soft shell of the well wall reinforcer facilitated the microspheres entry into the leading edge of induced fractures，while the calcium carbonate hard core dispersed stress and prevented further crack extension，effectively plugging the wellbore cracks. Additionally，it exhibited good compatibility with drilling fluids and excellent plugging performance.